Vertebrates are nothing but only animals with backbones; brain and spine is more complex. There are 5 well known classes of them: Mammals, Birds, Fish, Reptiles and Amphibians. All of them are a part of Phylum Chordata. They possess jawless fish and jawed vertebrates that further includes cartilaginous fish and bony fish. Invertebrates do not have an internal skeleton that is made of bone instead, they have a fluid-filled skeleton as of Jelly fish. Invertebrates do not have lungs, they respire through skin. They varies in size form 7.7mm (0.30 inches) to Blue whale 33m (108ft.)